Thermal transfer processes are well known in applications such as color proofing. Such thermal transfer processes include, for example, dye sublimation, dye transfer, melt transfer, and ablative material transfer, and typically use a laser to induce thermal transfer of matter. These processes have been described in, for example, Baldock, U.K. Patent No. 2,083,726; DeBoer, U.S. Pat. No. 4,942,141; Kellogg, U.S. Pat. No. 5,019,549; Evans, U.S. Pat. No. 4,948,776; Foley et al., U.S. Pat. No. 5,156,938; Ellis et al., U.S. Pat. No. 5,171,650; and Koshizuka et al., U.S. Pat. No. 4,643,917.
Laser-induced thermal transfer processes typically use a donor element including a layer of material to be transferred (“transfer layer”), and a receiving element including a surface for receiving the transferred material. The donor element and the receiver element are brought into close proximity or into contact with each other and selectively exposed to laser radiation, usually by an infrared laser. Heat is generated in the exposed portions of the donor element by the absorption of the incoming laser radiation, causing transfer of those portions of the transfer layer onto the surface of the receiving element. Either the substrate of the donor element or the receiving element (or both) are transparent. If the material of the transfer layer does not absorb the incoming laser radiation, the donor element must also include a heating layer adjacent to the transfer layer and a supporting base element. The heating layer is a material which absorbs radiation, generating heat to cause the transfer of the transfer layer. The donor element may also include additional layers, such as an ejection layer between the heating layer and the transfer layer. The ejection layer decomposes into gaseous molecules when heated. The gaseous molecules propel the exposed portions of the transfer layer to the receiving element.
In a digital process, the exposure takes place only in a small, selected region of the assembly at one time, so that transfer of material from the donor element to the receiver element can be built up one pixel at a time. Computer control facilitates high resolution and high speed transfer. Alternatively, in an analog process, the entire assembly may be irradiated and a mask may be used to selectively expose desired portions of the thermally imageable layer. See, for example, U.S. Pat. Nos. 5,857,709 and 5,937,272.
Organic electronic devices, such as light emitting devices, photodetecting devices and photovoltaic cells, may be formed of a thin layer of electroactive organic material sandwiched between two electrical contact layers. Electroactive organic materials are organic materials exhibiting electroluminescence, photosensitivity, charge transport and/or injection, (hole or electron), electrical conductivity, and/or exciton blocking. The material may be semiconductive. At least one of the electrical contact layers is transparent to light so that light can pass through the electrical contact layer to or from the electroactive organic material layer. Other devices with similar structures include photoconductive cells, photoresistive cells, photodiodes, photoswitches and transistors.
Organic electroluminescent materials which emit light upon application of electricity across the electrical contact layers include organic molecules such as anthracene, butadienes, coumarin derivatives, acridine, and stilbene derivatives. See, for example, U.S. Pat. No. 4,356,429 to Tang. Semiconductive conjugated polymers have also been used as electroluminescent materials. See, for example, Friend et al., U.S. Pat. No. 5,247,190, Heeger et al., U.S. Pat. No. 5,408,109, and Nakano et al., Published European Patent Application 443 861. The electroactive organic materials can be tailored to provide emission at various wavelengths.
Light sensitive devices, such as photodetectors and photovoltaic cells, may also use certain conjugated polymers and electro- and photo-luminescent materials to generate an electrical signal in response to radiant energy. Electroluminescent materials mixed with a charge trapping material, such as buckminsterfullerene (C60) and its derivatives, show such light sensitivity. See, for example, Yu, Gang, et al., “photovoltaic cells and photodetectors made with semiconductor polymers: Recent Progress”, Conference 3939, Photonics West, San Jose, Calif., Jan. 22-28, 2000.
Organic electronic devices offer the advantages of flexibility, low cost and ease of manufacture. (Id.) Their performance approaches and in some cases even exceeds that of traditional photosensitive devices. (Id.)
Organic semiconducting material may also be used to form thin film transistors. Transistors may now be fabricated completely from organic materials. Transistors of organic materials are less expensive than traditional transistors and may be used in low end applications where lower switching speeds maybe acceptable and where it would be uneconomical to use traditional transistors. See, for example, Drury, C. J., et al., “Low-cost all-polymer integrated circuits”, Appl. Phys. Lett., vol. 73, No. 1, Jul. 6, 1998, pp. 108-110. In addition, organic transistors may be flexible, which would also be advantageous in certain applications, such as to control light emitting diodes on a curved surface of a monitor. (Id.) Organic semiconducting materials include pentacene, polythienylene vinylene, thiophene oligomers, benzothiophene dimers, phthalocyanines and polyacetylenes. See, for example, U.S. Pat. No. 5,981,970 to Dimitrakopoulos et al., U.S. Pat. No. 5,625,199 to Bauntech, et al., U.S. Pat. No. 5,347,144 to Garnier, et al., and Klauck, Hagen et al., “Deposition: Pentacene organic thin-film transistors and ICs,” Solid State Technology, Vol. 43, Issue 3, March 2, on pp. 63-75.
Electroactive organic materials may be applied to one of the electrical contact layers or onto a portion of a transistor by spin-coating, casting or ink-jet printing. They may also be applied directly by vapor deposition processes, depending on the nature of the materials. An electroactive polymer precursor may also be applied and converted to a polymer, typically by heat. Such methods may be complex, slow, expensive, lack sufficient resolution and when patterned using the standard lithographic (wet development) techniques, expose the device to deleterious heat and chemical processes.
Ink jet printing has been used to apply pixels of electroactive organic material having diameters of about 350 to about 100 microns. See, for example, U.S. Pat. No. 6,087,196, EP 0880303A1, WO99/66483 and WO9943031. See also U.S. Pat. No. 5,989,945 for the use of ink jet printing to apply a resist. It has been claimed that pixels with diameters of about 35 microns have been applied in conventional printing applications such as short run color printing and the production of verification proofs for color reproduction.
Organic electronic devices such as photoemitting, photodetecting and photovoltaic devices typically include a layer of charge injection/transport material adjacent to the electroluminescent organic material to facilitate charge transport (electron or hole transport) and/or gap matching of the electroactive organic material and an electrical contact. Charge injection/transport materials have not been patterned. Charge injection/transport materials of low conductivity must therefore be used to avoid cross-talk between pixels.
Patterning materials using thermal transfer processes is generally faster and less expensive than patterning by using analog processes in combination with wet development techniques. Thermal transfer processes, particularly laser-induced thermal transfer processes, may also provide greater resolution. It would be advantageous to apply thermal transfer processes, particularly laser-induced thermal transfer processes, to the application of electroactive organic materials.